We have investigated the mechanism by which flavone-8-acetic acid (FAA) acts to enhance immune responsiveness in murine tumor model systems. Analysis of mRNA isolated from a mouse macrophage cell line after FAA administration indicates that both interferon-beta (IFN-beta), tumor necrosis factor (TNF), IL-6 and Interferon Response Factor-1 mRNA can be detected within 1-3 hours. These results indicate that FAA acts by directly stimulating gene expression of immunoregulatory proteins and not through the generation of metabolic intermediates.